using System.Text.RegularExpressions;
using CodePlay.Core.Interfaces;

namespace CodePlay.Core.Pipeline.Converters;

/// <summary>
/// C# 空合并/空条件运算符转换器
/// ?? → 三元表达式, ?. → null 检查, ??= → if-null 赋值
/// </summary>
public class NullCoalescingConverter : ILineConverter
{
    public int Priority => 45;

    public string Convert(string line, ConversionContext context)
    {
        var result = line;

        // ??= (null-coalescing assignment): x ??= value → if (x == null) x = value;
        result = Regex.Replace(result,
            @"(\w+(?:\.\w+)*)\s*\?\?=\s*(.+?)(;.*)?$",
            m => $"if ({m.Groups[1].Value} == null) {m.Groups[1].Value} = {m.Groups[2].Value};");

        // ?. (null-conditional): obj?.Property → (obj != null ? obj.Property : null)
        result = Regex.Replace(result,
            @"(\w+(?:\.\w+)*)\?\.(\w+(?:\s*\())",
            m => $"( {m.Groups[1].Value} != null ? {m.Groups[1].Value}.{m.Groups[2].Value}");

        // Nullable<T>.Value with ?.member → handled above
        // ?.Method() already handled by above pattern

        // ?? (null-coalescing): a ?? b → a != null ? a : b
        result = Regex.Replace(result,
            @"(\w+(?:\.\w+)*(?:\s+[=!<>]\s+[^;]+)?)\s*\?\?\s*([^,;\n]+)",
            m =>
            {
                var left = m.Groups[1].Value.Trim();
                var right = m.Groups[2].Value.Trim();
                return $"( {left} != null ? {left} : {right} )";
            });

        return result;
    }
}